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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: rmszymanski726 on March 09, 2014, 10:58:13 AM

Title: Help on Ka and pH problem
Post by: rmszymanski726 on March 09, 2014, 10:58:13 AM
I am attempting to solve this probelm but after trying several different methods (ICE table) I can't figure it out:
Sodium benzoate (C6H5CO2Na) is used as a food preservative.
a. Calculate the pH in 0.056M sodium benzoate; Ka for benzoic acid (C6H5CO2H) is 6.5×10−5.
b. Calculate the concentrations of all species present (Na+, C6H5CO−2, C6H5CO2H, H3O+ and OH−) in 0.056M sodium benzoate.
Title: Re: Help on Ka and pH problem
Post by: Borek on March 09, 2014, 01:37:31 PM
Let's start with a. Show what you did.
Title: Re: Help on Ka and pH problem
Post by: DanChen2014 on March 12, 2014, 02:02:11 AM
C6H5CO2- + H2O =====C6H5CO2H + H3O+

Kb=Kw/Ka
Title: Re: Help on Ka and pH problem
Post by: Borek on March 12, 2014, 03:31:57 AM
Quote from: DanChen2014 on March 12, 2014, 02:02:11 AM
C6H5CO2- + H2O =====C6H5CO2H + H3O+

Think it over.
Title: Re: Help on Ka and pH problem
Post by: DanChen2014 on March 12, 2014, 09:36:49 AM
Quote from: DanChen2014 on March 12, 2014, 02:02:11 AM
C6H5CO2- + H2O =====C6H5CO2H + H3O+

Kb=Kw/Ka
CORRECTION:
C6H5CO2- + H2O =====C6H5CO2H + OH-

YOU will have pOH.